The induction of pregnancy in female rats depends upon the copulatory behavior of the male. There are three major effects of the male's copulation: (1) His copulatory behavior, particularly the pre-ejaculatory intromissions, initiates the neuroendocrine reflex resulting in progesterone secretion necessary for gestation. (2) The pre-ejaculatory intromissions and deposition of a vaginal plug are necessary for the transport of sperm from the vagina into the uterus. (3) Post-ejaculatory copulatory stimulation, if it occurs too soon after the ejaculation, can disrupt this transport of sperm and thus interfere with fertilization and pregnancy. The research proposed in this application would continue our investigation into the mechanism and function of the behavioral influences on pregnancy in rats. We would investigate (1) the neural and endocrine mediators of the intromissions' induction of progesterone secretion, (2) the neurochemical meditors of the intromissions' effect on sperm transport, (3) the relationship of copulatory behavior to pregnancy induction in wild rats living in semi-natural conditions, (4) the physiological basis of reproductive motivation in male and female rats, especially as this is related to maintaining pregnancy and maternity, and (5) the relationship of reproductive cyclicity to somatic cyclicity.